Heat-treating furnace



1954 G. M. TAUBER ETAL HEAT-TREATING FURNACE 3 Sheets-Sheet 2 Filed Oct.14. 1950 INVENTORS. GUSTAVE M. TAUBER JOHN J. SCHULTZ ATTORNEYS g 17,1954 G. M. TAUBER ETAL HEAT-TREATING FURNACE 3 Sheets-Sheet 3 Filed ON.14. 1950 4 00 sec 000 I IOIOOI lz oo m oo leoo Temperature DegreesFahrenheit I000 I200 I400 I600 300 Temperature Degrees FahrenheitINVENTORS. GUSTAVE M. TAUBER BY JOHN J. SCHULTZ ATTORNEYS Patented Aug.17, 1954 HEAT- TREATING FURNACE Gustave M. Tauber, Philadelphia, andJohn J. Schultz, Drexel Hill, Pa., assignors to Leeds and NorthrupCompany, Philadelphia, Pa., a corporation of Pennsylvania 1 ApplicationOctober 14, 1950, Serial No. 190,152

This invention relates to heat-treating furnaces of the forcedconvection type used for tempering, annealing, carburizing, nitridingand similar heat-treating processes.

In many furnaces of this type, a fan, disposed in the bottom of thefurnace below an open- 3 Claims. (Cl 266-) ended basket which containsthe work to be 1 treated, forcibly circulates the furnace atmosphererepeatedly through the work container and a heating space between thework container and the internal wall of the furnace.

In accordance with the present invention, en-

closure of the fan and support of the work container is provided by acasing structure essentially comprising. an apertured plate forming theupper wall of a fan housing and from which downwardly extend a pluralityof vanes whose lower edges rest upon the furnace base, thus to form fandischarge outlets or ducts opening into the heating space of thefurnace. Further and more specifically in accordance with the invention,a peripherally continuous sealing skirt extends upwardly fromtheapertured plate with its upper portionforming a supporting ring orflange for the bottom of the work basket or tray. More particularly, aremovable screen passed by the sealing skirt overlies the fan inletopening or openings in the apertured plate and is preferably positionedby bracing ribs of the sealing skirt.

Further in accordance with theinvention, the fan outlet vanes extendbeyond the sealing skirt with the upper edges of the vane extensionsrespectively joined to projecting areas of the apertured plate.

Further in accordance with the invention, the fan housing is providedwith members extending upwardly from it to center the work containersupported thereon with respect to the sealing skirt and fan inlet; more.specifically, the lower and vertical portions of the center membersrespectively merge with the apertured plate and with the sealing skirtto impart additional strength and rigidity to the entire unit.

The invention further resides in novel and useful features ofconstruction, combination and arrangement. 1

For a more detailed understanding of the invention and for illustrationof the embodiments thereof, reference is madeto the accompanyingdrawings, in which:

Fig. 1 is a side elevational view, in section, of one type of furnaceutilizing thenew fan housing andwork support unit; 1

Fig. 2 is a bottom view of the fan housing unit of Fig. 1;

Fig. 3 is a top plan view, on enlarged scale, of the fan housingstructure of Fig. 2; 1

Fig. 4 is an elevational view, partly in section, of the housing shownin Fig. 3;

Fig. '5 is a perspective view of the fan housing of Figs. 2- 1;

Figs. 6A and 6B are explanatory figures referred to in discussion of afurnace embodying the new fan housing; and

Fig. 7 is a perspective view, partly broken away, of another type offurnace utilizing the housing structure of Figs. 1-5.

In Fig. 1 there is shown a heat-treating furnace l 0 of type generallyshown in United States Letters Patent including 2,176,473; 2,168,028;2,161,162; 2,032,209; 1,999,757; 1,926,234; 1,949,- 716; 1,940,948; and1,721,840. In brief, the work to be treated is disposed in a workcontiner H whose upper and lower ends are open and whose sidewalls areimperforate. The grid l2 in the bottom of the work basket, tray orequivalent container ll provides support for the work pieces and yetpermits free passage of the furnace atmosphere. As later more fullydiscussed, the work container rests upon and is supported by a fanhousing structure l3 disposed in the bottom of the heat-treating chamberI 4 defined by the base member I5, the retort 16, or equivalent internalwall structure of the furnace, and the removable cover member I! whichserves: as a removable closure for the top of the heat-treating chamber14.

The cover I! is provided with a downwardly directed flange which isreceived by the channel It at the upper end of retort l6 and filled withsand or other sealing material to prevent escape from chamber [4 of thefurnace atmosphere.

The furnace may be gas-fired or electrically heated as shown byaforesaid patents; in the particular furnace shown in Fig. 1, thefurnace atmosphere and work are raised to treating temperature by theelectrical heater elements l9 suitably supported by the wall structure20 of the furnace which like base member I5 is of heat-insulating brickand refractory. To minimize heat losses, the cover of the furnace issimilarly provided with an outer layer 2| of heatinsulting brick orequivalent.

In the preferred arrangement shown in Fig. 1, the furnace retort I 6 hasa closed bottom and is supported by the ring or flange provided by theextension of the bottom plate 22 of the furnace beyond the side wallstructure 2! In this respect the construction differs from that ofaforesaid patents in which the retort has an open bottom with the loweredge received by a sand seal.

For forcible circulation of the furnace atmos phere within the treatingchamber i l so defined, there is provided a fan 23 supported below theopen bottom of the work container l l by attachment to the upper end ofa motor shaft 2 which extends through the base it. Escape of furnace gasalong shaft 24 is precluded by a suitable sealing gland. The shaft M isdriven by motor 25 suitably suspended as by bolts 25 from the underfaceof the furnace base member it which in the embodiment of Fig. 1 iswithin the retort so that the base It, motor 25, fan 23 and the combinedfan-housing and container support it are insertable into and removablefrom the furnace as a unit with the retort.

As shown more clearly in Figs. 2-5, the housing [3 for the fan 23comprises a plate ill which forms the upper wall of the fan housing.This plate is provided with a central opening it of diameter suitablyless than the diameter of the fan 23 or otherwise suitably apertured toprovide a fan inlet. From the underface of plate 2? there downwardlyextends a plurality of vanes 29, whose lower edges are free to engageand rest upon the upper face of the base member is of the furnace, asshown in Fig. 1. The inner edges 8| of the vanes 25 define a circle ofdiameter slightly greater than the fan circle, and the outer edges 32 ofthe vanes define a circle approximately circumscribed by the retort l5.Thus, when the housing It is in place, the vanes 29 in coaction withplate El or the housing and base lb of the furnace form fan outletsdischarging into the gas-heating space between the retort it and thework container ll. Preferably and as shown, the fan 23 is of thecentrifugal type and the vanes 29 extending substantially tangent to thefan circle are of spiral or volute form.

As shown most clearly in Figs. 2-5, the vanes 29 project beyond the maincircular area of the plate 2? but are respectively joined to that areaby minor areas 33 of approximately triangular shape. These minor areas33 serve as upper walls of the fan outlet ducts and also as barrierswhich prevent dislodged work objects from entering the fan housing.Objects which fall in the gaps between these areas fall on the flat upper surface of the base l5 below the fan and externally of the housingand so do not damage the fan.

Preferably and as shown, from the main annular area of the plate 2?there upwardly extends a sealing skirt of outline substantiallycorresponding with that of the work container and having a flange 35,preferably inwardly directed, peripherally to engage the lower edge ofthe work container for support of the container and its load. Thus, theopening till provided by the flange 35 closely approximates the area ofthe opening in the bottom of the work container for free flow of thefurnace atmosphere.

The sealing skirt 3G is stiffened to resist de formation by the weightof the work basket and its contents at the high temperatures involved inheat-treatment by series of bracing ribs 36 which extend inwardly fromthe inner periphery of the sealing skirt 3 3. The inner ends oi thesealing ribs serve as steps or centering lugs for positioning aprotective screen above the 4 fan inlet opening 28 in the upper wallplate 21 of the fan housing. The opening 39 defined by the flange 35 ofthe sealing skirt is of larger diameter than the screen 38 to permiteasy removal of the screen.

For centering of the work basket II] as it is lowered into the furnaceretort for engagement with the fan housing E3, the housing is providedwith a plurality of basket-centering members 59 having upper portionswhich extend upwardly and outwardly from the upper portion of thehousing l3. Specifically, the lower portion of each of the centeringmembers 48 merges with a projecting area 33 of the plate 27, and theinner vertical edge of the lower portion of each of the centeringmembers merges with the periphery of the sealing skirt 35: the centeringmembers therefore also serve to strengthen and stiffen the fan housingstructure. As most clearly appears in Fig. 3, the centering members 40and the ribs 33 are angularly spaced about the periphery of the sealingskirt to afford distribution of the stiffening eifects.

The fan housing and basket support I 3 is preferably cast as a unitarystructure although it may be fabricated from components welded togetherto form a unitary structure. For long life, the housing it should be ofmetal resistant to the furnace gases and temperatures.

The fan housing and work basket support l3 not only is of advantage inconstruction and maintenance of the furnace, but also is of operationaladvantage in that temperature uniformity of a fresh work charge withinthe container II is more rapidly attained. Referring to Fig. 6A, thecurve A represents the temperature of work at zone #6 of the workbasket, the coolest zone during initialheating, and curve B representsthe temperature of work in zone #1, the hottest zone during the initialheating. As apparent from Fig. 6A, hich is based upon measurements in afurnace not using the present invention, a substantial difference oftemperature exists between these two zones for the initial heatinginterval T preceding arrival of these zones at the control point ordesired heat-treating temperature which in the particular caseillustrated is 155i)". With the same furnace construction using,however, the improved fan housing, the temperature difference betweenthe hottest and coolest zones of the furnace during the initial heatingsignificantly is less as shown by the narrowed gap between curves A andB of Fig. 63. For example, with fan housing E3, the work in furnace zone#6 attained a temperature of about 500 when the temperature in zone #1was about 250 higher (Fig. 63), whereas with the prior arrangement, bythe time the work in zone #6 had attained a temperature of 500 the workin zone was 350 higher (Fig. 6A). Moreover, with the prior arrangement,when the hot zone temperature reached the control point, the temperaturespread in the work basket was about (Fig. 6A), whereas with the newarrangement the emperature difference upon arrival at the control pointis only about .6". This feature of the new fan housing is particularlyof advantage for short runs, as in tempering, because affordingincreased furnace output without sacrifice of uniformity of product.

For some heat-treating operations, the furnace atmosphere forciblycirculated by the fan is essentially air; for other heat-treatingprocesses, the furnace atmosphere may comprise or consist of a gas, orgases, inert or active. For use of treating atmospheres other than air,there is provided, as more fully shown in certain of the aforesaidpatents above identified, an inlet 42 (Fig. 1) for admission of thetreating gas or source thereof. A sight gauge 43 may be provided whenliquid is fed in drops into the fur nace for vaporization and liberationof active gaseous agents. An exhaust pipe 44 is provided for escape ofthe partially depleted furnace atmosphere, a hinged cap 45 beingprovided to permit insertion and removal of test samples, if desired,during a heat-treating cycle.

Use of the fan housing and work support [3 is not restricted to thetop-loading cylindrical type shown in Fig. 1 and may be to advantageused in box furnaces which are side or frontloaded. In Fig. 7,illustrative of one type of box furnace, the fan housing I3 is disposedwithin the furnace with the lower edges of its vanes 29 resting upon theupper face of the furnace base [5A. The base, as in Fig. 1, thus formsthe lower wall of the fan housing and coacts with the vanes of thehousing to define fan discharge ducts which open into the heating spaceof the furnace between the furnace side walls and the work containerresting upon the flanged upper edge of the sealing skirt 34. In bothFigs. 1 and 7 the fan housing is held against the furnace base by boltsor equivalent securing means which engage hold-down lugs 4| extendingfrom at least some of the vanes. In Fig. 7, the upper edge of thesealing skirt 34 is approximately in the same plane as the lower edge ofthe opening 46 in the front wall of the furnace. Thus, a work basket. orcontainer may be slid through the opening onto the fan housing. Ifdesired, rails or guides may be provided to facilitate this loadingoperation. When used ina box furnace, some of the members 40 may beomitted to avoid obstruction to the work basket as: it is slid onto thesealing skirt though at least one of the members 40 may be retained toserve as a rear stop 40A for the work basket.

It will be understood by those skilled in the art that the invention isnot limited to the specific embodiment shown and that changes andmodifications may be made within the scope of the appended claims.

What is claimed is:

1. For use in a heat-treating furnace having adjacent its base a fan forforcibly circulating the furnace atmosphere repeatedly through aremovable work-container having an open bottom of area substantiallycoextensive with the crosssectional area of the container, a unitarystructure forming a fan housing and a work-container support comprisinga sealing skirt member having an upper edge for peripherally engagingthe bottom edge of the work-container and defining an openingsubstantially coextensive with said open-bottom area of thework-container, a plate member joined to the lower edge of said skirtmember to form the upper wall of the fan housing and apertured withinthe fan diameter, and a plurality of vanes attached to and extendingdownwardly from said plate member for engagement with the furnace basewhich thereupon forms the lower wall of the fan housing and supportssaid unitary structure, said vanes extending tangentially of the fandiameter to project beyond the periphery of said sealing skirt and thework-container, said plate member having substantially triangularextensions respectively closing the gaps between the upper projectingedges of the vanes and the sealing skirt member.

2. An arrangement as in claim 1 in which the outer vertical edges of thevanes of said unitary structure define a circle closely circumscribed bythe periphery of the inner wall structure of the furnace for freedischarge from said outer vertical edges of the fan into the heatingspace between said wall structure and the work-container.

3. An arrangement as in claim 1 in which spaced bracing ribs extendinwardly of the sealing skirt and upwardly of the plate member, theinner ends of said ribs terminating short of the aperture through saidplate member, and in which a screen passed by the opening in the sealingskirt member is positioned by said ends of the bracing ribs to overliethe aperture through the plate member.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 126,639 Leffel May 14 1872 1,870,551 Brown Aug. 9, 19321,976,557 Haskell Oct. 9, 1934 2,168,028 Harsch Aug. 1, 1939 2,245,647Burby June 17, 1941 2,249,411 Woodson July 15, 1941 2,463,222 VaughanMar. 1, 1949 FOREIGN PATENTS Number Country Date 673,878 Germany Mar.3!), 1939

